A resectoscope for visually observing and performing transurethral resection of pathological changes at the prostate and bladder has a cutting loop assembly having spaced parallel insulated arms which at their distal ends support a depending bare wire loop which is activated by high frequency electrical current and which performs the cutting operation. Arcing between the distal ends of the arms or the upper ends of the depending loop and the adjacent distal end of the telescope tube often occurs when the cutting loop is moved to rest position, with consequent damage to the parts and adverse effect of the operative procedure.
A resectoscope having parts of conventional construction is disclosed in FIG. 1 as background for disclosure of the invention, and comprises the tubular sheath 2 which provides a passageway through the human urethra to the area of visual and operative interest, and which has at its distal end a beak 4 which is formed of an electrically insulating material such as a synthetic plastic and the shape of which is such that the side walls thereof recede in the proximate direction from the upper part of the distal end of the beak to the lower part. At its proximate end the sheath has a socket base 6 at which there is a tube 8 with stopcock 10 for the introduction of clear irrigating fluid, and a thumb screw 12 for attaching the sheath's socket to the working element 14 for reciprocally moving the cutting loop assembly and electrode between protracted and retracted positions longitudinally of the telescope stem in performing an operation. Within the sheath are the telescope stem 16 and the cutting loop electrode assembly 18.
The telescope has an objective lens 22 at its distal end and an ocular lens (not shown) and eyepiece 24 at its proximal end. Light conductors (not shown) extend through the telescope from an external connection 26 to the distal end for providing illumination. The field of vision at the operative field with the objective lens positioned as shown in FIG. 1 is illustrated by the broken lines shown in that figure and its shape is that of a truncated cone with the truncated surface at the objective lens.
The cutting loop electrode assembly 18 disclosed in FIGS. 1 and 2 comprises the elongated hollow stem 28 from the distal end of which there protrude two parallel arms 30, 32 which are insulated wires positioned on opposite sides of the telescope adjacent its distal end, and which are connected at their distal ends by a depending semi-circular bare wire cutting loop 34 which is activated by high frequency electrical energy to resect pathological tissues and coagulate bleeding vessels. The stem 28 and arms 30, 32 transmit electrical energy and the reciprocating movement of the working element 14 to the cutting loop 34.
FIG. 1 shows the bare wire cutting loop 34 in its conventional position extending downwardly at 90.degree. to the spaced parallel insulated arms 30, 32 of the cutting loop assembly. Those arms are of such length that when the cutting loop assembly is retracted into the beak of the sheath during an operative procedure, as shown in FIG. 1, the bottom of the loop enters the beak in close proximity to the inner surface of the bottom wall of the beak, thus completing the resection of tissue, which is the object of the procedure.
Resectoscopes are now being provided with a telescope having the rod type lens which increases the total light and resolution at the operative field, and having a wider angle of vision than older types, because of which the distal end of the telescope must be very close to the beak of the sheath in order to prevent impairment of the field of vision by the end wall of the beak. As stated, the bare wire cutting loop must enter the insulated beak of the sheath in close proximity to its inner wall in order to complete a resection and this requirement, in conjunction with the distal extension of the telescope tube for visual reasons, has caused electrical arcing between the upper ends of the bare wire cutting loop and the distal end of the telescope, with consequent damage to the telescope, which is the most important and expensive part of the instrument, and adverse effect on the operative procedure. Among the methods suggested to correct this difficulty are (1) positioning the distal end of the telescope backward within the sheath beyond the position of optimum vision, (2) reducing the proximal movement of the cutting loop assembly in order to maintain the bare wire cutting loop at a safe distance from the telescope tube, and (3) extending the insulation of the spaced parallel arms of the cutting loop assembly over and beyond the junction of the arms and the depending loop. None of these has been satisfactory and none has prevented arcing, and the object of my present invention has been to prevent arcing while at the same time maintaining the increased illumination and field of vision provided by modern telescopes of resectoscopes, and insuring that the cutting loop will co-operate with the sheath in completing a resection.